The present invention relates to an electric driving device for a transmission. An electric driving device for a transmission according to the present invention is suited to be utilized as a driving device for changing a gear ratio of a transmission of a car automatically or under an instruction from the driver.
Hitherto, as a transmission of a car, there is widely employed a manual transmission with which the driver changes gears by operating a shift lever, together with a clutch pedal, or an automatic transmission for automatically changing gears in accordance with a situation. Out of these types, for an automatic transmission, a combination of a torque converter and a planetary gear mechanism, a combination of a variable-type pulley and an endless belt, and the like, are conventionally used. Furthermore, a transmission for a car which allows automatic switching of a gear unit conventionally serving as a manual transmission and automatic disconnection of the clutch is recently used since it is easily to operate and has a higher efficiency in transmission, compared with an ordinary automatic transmission. As a structure for changing the gears constituting a gear unit in such an automatic transmission, there are conventionally known a hydraulic type and a mechanical type as disclosed in Japanese Patent Application Laid-Open No. 2-273051.
In a structure in which hydraulic is used to change the gears for constituting a gear unit, like in the conventional structure, a power loss is generated since a hydraulic pump is driven to rotate all the time during the drive of a car, which not only exercises a bad influence on the running performance or the cost performance of the car, but also requires extra works for preventing a fault which may be caused by oil leakage. A device which is conventionally known for mechanically performing the above switching has been developed for large-sized vehicles such as a tractor, so as to have a complicated arrangement and require a wider space to be installed, which is unsuitable for small-sized vehicles like a passenger car.
An electric driving device for a transmission of the present invention has been contrived taking such circumstances into consideration.
According to a first aspect of the present invention, there is provided an electric driving device for a transmission which is characterized in that:
a selecting operation for displacing a shift shaft in the axial direction so as to select a desirable gear out of a plurality of gears and a shifting operation for rotating the shift shaft so as to bring the selected gear into a meshing state are performed by a first and second actuators respectively employing electric motors as the driving sources thereof;
the first actuator for performing the selecting operation comprises a first electric motor, a worm gear to be driven to rotate by an output shaft of this first electric motor, a worm wheel to be meshed with this worm gear, and a rocking arm for rotating together with this worm wheel, the tip end of this rocking arm being engaged with a part of the shift shaft to allow this shift shaft to be displaceable in the axial direction upon rocking of this rocking arm;
the second actuator for performing the shifting operation comprises a second electric motor, and a ball screw mechanism equipped with an output shaft member to be driven to rotate by an output shaft of this second electric motor for issuing an output converted into a rectilinear motion; and
the tip end of this output shaft member is coupled to the tip end of a driving arm for rotating the shift shaft so that the driving arm is rotated by the rectilinear motion of the output member to rotate the shift shaft, thereby performing the shifting operation.
According to a second aspect of the present invention, there is provided an electric driving device for a transmission which is characterized in that:
a selecting operation for displacing a shift shaft in the axial direction so as to select a desirable gear out of a plurality of gears and a shifting operation for rotating the shift shaft so as to bring the selected gear into a meshing state are performed by a first and second actuators respectively employing electric motors as the driving sources thereof;
the first actuator for performing the selecting operation comprises a first electric motor, a rotation transmitting member to be driven to rotate by an output shaft of this first electric motor and having peripheral teeth, a rotation receiving member having peripheral teeth substantially in parallel to the shaft of the rotation transmitting member to be meshed with the peripheral teeth of the rotation transmitting member, and a rocking arm for rotating together with this rotation receiving member, the tip end of this rocking arm being engaged with a part of the shift shaft to allow this shift shaft to be displaceable in the axial direction upon rocking of this rocking arm;
the second actuator for performing the shifting operation comprises a second electric motor, and a ball screw mechanism equipped with an output shaft member to be driven to rotate by an output shaft of this second electric motor for issuing an output converted into a rectilinear motion; and
the tip end of this output shaft member is coupled to the tip end of a driving arm for rotating the shift shaft so that the driving arm is rotated by the rectilinear motion of the output member to rotate the shift shaft, thereby performing the shifting operation.
According to a third aspect of the present invention, the electric driving device for a transmission according to the first and second aspects is characterized in that:
the ball screw mechanism comprises a ball screw shaft to be driven to rotate by the second electric motor, and the output shaft member disposed around this ball screw shaft for moving in the axial direction of the ball screw shaft upon rotation of the ball screw shaft.
According to a fourth aspect of the present invention, the electric driving device for a transmission according to the first and second aspects is characterized in that:
the ball screw mechanism comprises a ball nut to be driven to rotate by the second electric motor, and a ball screw shaft to be engaged with this ball nut through a ball for moving in the axial direction upon rotation of the ball nut; and
the ball screw shaft serves as the output shaft member.
According to a fifth aspect of the present invention, there is provided an electric driving device which is used for a transmission for performing a selecting operation for displacing a shift shaft in the axial direction so as to select a desirable gear to bring it into a meshing state and a shifting operation for rotating the shift shaft so as to bring the selected gear into a meshing state, comprising:
an electric motor;
a ball screw mechanism having an output shaft member for converting a rotation output of the electric motor into a rectilinear motion and outputting this rectilinear motion, the output shaft member arranged to be coupled to a rocking driving arm of the shift shaft to rotate the shift shaft; and
a detent mechanism for locating the output shaft member at a neutral position so as to give a predetermined resistance when the output shaft member is moved from the neutral position.
The electric driving device for a transmission of the present invention arranged as described above switches the gears of a gear unit in the following manner. First, the first electric motor for constituting the first actuator is rotated in a predetermined direction to rock and displace the rocking arm. Then, the shift shaft is displaced in the axial direction along a predetermined direction from the tip end of this rocking arm, so as to perform the selecting operation. Since the power required for this selecting operation is small, even when a displacing speed of the rocking arm is secured by meshing the worm gear with the worm wheel, or by meshing the rotation transmitting member with the rotation receiving member (both members are respectively disposed substantially in parallel to each other and provided with the peripheral teeth), the selecting operation can be satisfactorily performed without using a motor capable of a particularly large output as the first electric motor.
After the selecting operation is thus performed, the shift shaft is rotated by the second actuator through the driving arm in order to perform the shifting operation. Though this shift operation is performed by moving the output shaft member of the ball screw mechanism for constituting the second actuator in the axial direction through this ball screw mechanism, the power for thus moving the output shaft member in the axial direction through the ball screw mechanism can be made satisfactorily large. As a result, the shifting operation which requires a larger power, compared with the selecting operation, can be performed without fail.
The meshing state between the worm gear and the worm wheel or that between the rotation transmitting member and the rotation receiving member for constituting the first actuator is arranged to be reversible, and the engaging state with the ball screw mechanism for constituting the second actuator is also reversible. Accordingly, even when the drive of the shift shaft can not be performed by these first and second electric motors due to a fault of these first and second electric motors, it is possible to drive this shift shaft manually.